Process for Preparing Crosslinked Polymer-Carbon Sorbent

ABSTRACT

A polymer-carbon sorbent for removing at least one of carbon dioxide, heavy metals or toxic materials from a flue gas from a combustion process, such as coal-fired power plants, is described. The sorbent comprises a carbonaceous sorbent material and a cured amine-containing polymer, and sulfur. The polymer-carbon sorbents are formed by curing a curable amine-containing polymer in the presence of the carbonaceous sorbent material, sulfur, a cure accelerator and, optionally, a cure activator. A convenient carbonaceous sorbent material is an activated carbon, and a convenient curable amine-containing polymer is an allyl-containing poly(ethyleneimine), having a number average molecular weight between about 1,000 and about 10,000. The polymer-carbon sorbents may contain sulfur in molar excess of an amount needed to cure the curable amine-containing polymer. Such polymer-carbon sorbents are shown to capture more mercury, in both elemental an ionic forms, compared to activated carbon and adsorb carbon dioxide.

RELATED APPLICATIONS

The present application is a division of U.S. Ser. No. 13/585,172, filedAug. 14, 2012, which is a continuation-in-part of and claims benefit ofPCT/US2011/025583, filed 21 Feb. 2011, which claims benefit ofPCT/US2010/000501, filed 22 Feb. 2010.

BACKGROUND

1. Field of Invention

This invention relates to polymer-carbon sorbents suitable for removingheavy metals and toxic pollutants from flue gas, and adsorption ofcarbon dioxide. More specifically, this invention relates to apolymer-carbon adsorbent comprising a cured amine-containing polymer anda carbonaceous sorbent material to reduce emissions of elemental mercuryand oxidized mercury and carbon dioxide from coal-fired power plants.

2. Description of the Related Art

Many heavy metals, especially mercury, are both hazardous and poisonous.Consequently, there is frequently a need to remove heavy metals,including mercury, from air streams around industrial processes such aschlor-alkali plants, iron ore processing, steel manufacturing, miningoperations, and electronics manufacturing operations.

Mercury is a chemical of global concern specifically due to its longrange environmental transport, its persistence in the environment onceintroduced, its ability to bio-accumulate in ecosystems, and itssignificant negative effects on human health and the environment.Mercury can be present in both liquid and gaseous waste streams. Mercuryin gas streams provides additional challenges because of the volatilityof metallic mercury and its compounds, which results in small quantitiesof mercury vaporizing from the heat of industrial processes, the burningof incinerator waste, and the burning of mercury-containing fuels.

Several approaches have been developed for effectively removing mercuryspecies and other heavy metals from various streams. These overallapproaches include, among others: liquid scrubbing technologies,homogenous gas-phase technologies, metal amalgamation techniques, andprocesses using various sorbent materials in different applicationschemes.

Capturing and isolating gaseous, elemental mercury from coal-fired powerplants is a difficult technical problem because the gas volumes involvedare great, the concentrations of mercury in the gas are low, and the gastemperatures are relatively high. Mercury typically exists as a traceelement in coal, about 0.1 ppm by weight, although this can vary betweencoal types. As coal burns, the mercury volatilizes to formthermodynamically favored gaseous elemental mercury, Hg⁰. In thesubsequent cooling of the combustion gases, interaction with othercombustion products results in a portion of the elemental mercury beingconverted into gaseous oxidized form of mercury, Hg₂ ⁺² and Hg⁺² ions.Oxidation makes mercury easier to remove in a wet scrubber system,because most of the compounds formed from oxidized mercury arewater-soluble, although toxic. The Hg⁰ is difficult to control, and islikely to enter the atmosphere because of its high vapor pressure andlow water solubility. Small portions of Hg⁰, Hg₂ ⁺², and Hg⁺² absorbonto residual particulates, such as fly ash, forming particle-boundmercury (Hg^(P)) that can be removed by filter or electrostaticprecipitator.

A common practice for both gas and liquid removal of heavy metals is tocontact the gas or liquid with a solid sorbent. “Sorbents” is a moregeneral term used collectively for absorbents, which draw the heavymetal into their inner structure; adsorbents, which attract heavy metalsand holding them to their surfaces; and chemisorbents, which form bondsbetween the surface molecules of the sorbent and the heavy metal speciesin a liquid or gas. Sorbents are typically in the form of particles,powders, or granules. Finely divided or microporous materials presentinglarge areas of active surface are strong adsorbents. Common adsorbentsinclude activated carbon, activated alumina, and silica gel. Somesorbents, because of their size, shape, pore size, or chemicaltreatment, use more than one mechanism for removal of heavy metals. Forexample, some adsorbents may be treated or modified with materials,forming chemisorbents that will react with a heavy metal species.

Activated carbons are useful sorbents for sequestering mercury vapors inmany applications, and have been studied extensively for use in fluegases. In small-scale gas processing, activated carbons may be used infixed bed reactors or columns. However, for applications having largevolumes of hot gas, such as coal-fired power plants, a fixed bed reactoror column may have cost issues associated with a large pressure drop,and maintenance of a fixed bed or column.

A number of inventive methods have been developed to apply mercurysorbent technologies to the large-scale gas streams of coal combustionfor power generation. Moller et al., U.S. Pat. No. 4,889,698, and Chang,U.S. Pat. No. 5,505,766, for example, both describe the injection offine powdered activated carbon (PAC) into flue gases at points alongtheir journey through various pollution-control equipment trains. ThePAC was then captured by a fabric filter. However, only about 15% ofcoal-fired boilers in the United States have such fabric filters, whichallow for a high degree of mass transfer as the mercury-laden flue gasthrough a layer of the sorbent on the fabric filter bags. On the otherhand, about 65% of United States coal-fired utility boilers haveelectrostatic precipitators (ESPs) instead of fabric filters, with nodesulfurization systems for flue gases. An ESP configuration requiresin-flight mercury removal, with some amount of time on the ESP platesparallel to the gas flow. That is, ESP configuration typically has lessmass-transfer available to remove mercury vapor, compared to a flow offlue gas through a fabric filter.

Nelson, in U.S. Pat. No. 6,953,494, incorporated herein by reference,teaches a mercury-control method that can be applied to a number ofcombustion gas streams and a wide range of exhaust systemconfigurations. Nelson teaches that activated carbon treated withbromine provides a more effective mercury sorbent material thanuntreated carbon or carbon treated with other halides. Bromine oxidizesthe elemental mercury to toxic water soluble He⁺²salt. Nelson's mercurytreated activated carbon sorbent is especially suitable for in-flightremoval of mercury. Nelson describes several configurations for use ofin-flight removal of mercury that demonstrate the temperatures andcontact times used in such processes.

FIG. 1 through 4 are schematic diagrams of exhaust gas systemsdescribing example methods for using sorbents to remove and sequestermercury from hot combustion gases.

FIG. 1 shows an example system that applies mercury sorbents to acombustion gas stream where a fabric filter (baghouse) is utilized tocollect fly ash generated during combustion. Coal, industrial wastes, orother fuels are combusted in a boiler 11 generating mercury-containingflue gas, which is cooled by steam tubes and an economizer 21. Flue gastypically then flows through ductwork 61 to an air cooler 22, whichdrops the gas temperature from about 300-to-400° C. down to about150-to-200° C. and exits the air cooler in ductwork 62.

A mercury sorbent, stored in a container such as a bin 71, is fed to andthrough an injection line 72 to the ductwork 62 and injected through amultitude of lances to be widely dispersed in the hot combustion fluegas. Mixing with the flue gas, the sorbent adsorbs target heavy metalspecies, elemental mercury and oxidized mercury species from the fluegas. The sorbent flows with flue gas to a fabric filter 31 and isdeposited on the filter bags in a filter cake, along with the fly ashand other gas-stream particulates. In the fabric filter the flue gas isforced through the filter cake and through the bag fabric. The flow offlue gas through the filter cake causes intimate contact between thesorbents and the remaining mercury in the flue gas, and will result in ahigh degree of mercury capture with a high degree of utilization of thesorbents. Cleansed of its mercury content and particulates, the flue gasexits the fabric filter 31 to ductwork 63, a smokestack 51, and then tothe atmosphere. Upon cleaning of the fabric filter bags, the mercurysorbents in the filter cake fall into hoppers and are eventually emptied81 from the fabric filter 31, and are disposed of along with thecollected fly ash and unburned carbon. The mercury sorbents willgenerally make up on the order of 1 wt % of the collected particulatesin pulverized coal power-plant applications.

FIG. 2 describes an example application of sorbents to a plant which has“cold-side” electrostatic precipitator (ESP) 32 instead of a fabricfilter. Using an ESP provides a more difficult situation for mercuryremoval than with a fabric filter, because flue gas is not forcedthrough the mercury sorbent in a filter cake layer of a collection bag.The hot mercury-containing combustion gas is generated in the boiler 11,as in FIG. 1, and flows through the same equipment to the ductwork 62.The mercury sorbent of bin 71 is similarly injected 72 into the ductworkto mix with the flue gas. Because of poorer mass transfer within the ESP32, however, it is particularly important to inject at 72 as far aheadof any turning vanes, flow distributors, ductwork, and other exposedsurface-area in the ductwork as possible. This not only provides moreresidence time for the sorbents to mix with and remove mercury from theflowing gas, but provides for more mass transfer area for the sorbent tocollect on, further increasing the overall mass transfer and mercuryremoval. In the ESP 32, the sorbents are collected on plates with thefly ash and upon rapping of the plates are eventually discharged 81 fromthe ESP 32 for disposal along with the rest of the particulates.

Several variations on arrangements of FIGS. 1 and 2 might be suggested,based on a configuration of existing air pollution control equipment.For example, a wet scrubber for flue gas desulfurization could appear at63 in FIGS. 1 and 2 or a particulate scrubber could replace ESP 32.Selective catalytic reduction (SCR) units for NO_(x) reductions, whichalso can reduce Hg⁺² to elemental mercury or flue gas conditioningsystems to improve particulate removal, could also be placed in theequipment arrangements. Similarly, mercury sorbents could be injectedwhile mixed in with sorbents for other flue gas components, such ascalcium or magnesium hydroxide or oxide for flue gas SO₃, HCl, or SO₂,rather than injected alone. Alternately, the mercury sorbents could beinjected in liquid slurry, which would quickly evaporate in the hot fluegas.

FIG. 3 applies the sorbents in a TOXECON® arrangement, a processpatented in U.S. Pat. No. 5,505,766, and marketed by Electric PowerResearch, Inc., Palo Alto, Calif. Mercury sorbents 71 are injected afteran ESP 32 into almost particulate-free ductwork 67 before a small,high-velocity fabric filter 33. In this manner the fly ash 80 does notbecome mixed with the carbonaceous sorbents, allowing the fly ash to besold for concrete use. Moreover, the filter cake of fabric filter 33would predominantly be mercury sorbent, allowing a longer residencetime, higher utilization levels, and the possibility of recovering andre-injecting the sorbent to lower costs.

FIG. 4 illustrates sorbent usage at plants that have spray dryers foracid rain control. A mercury sorbent could be injected 62 before thespray dryer 41, into the spray dryer 41, into the ductwork 68, betweenthe spray dryer and the particulate collector 31 or 32, or mixed in withthe scrubber slurry itself.

Mercury has a high affinity for sulfur. Elemental mercury, in thepresence of sulfur, readily forms mercury (II) sulfide when heated.Mercury (II) sulfide can exist in two chemically stable forms: a red,hexagonal complex (cinnabar), and a black metastable structure(metacinnabar). Mercury also readily forms complexes with other sulfurcompounds, including sulfates (HgSO₄), dithiocarbamates (Hg(Et₂DTC)₂)and various thioethers (Hg(SR)₂). The affinity of mercury for sulfur haslead to many studies of sulfur-treated carbon adsorbents for the removalof mercury. See, for example, Bylina et al., Journal of Thermal Analysisand calorimetry (2009), 96(1), pp 91-96 “Thermal analysis of sulfurimpregnated activated carbons with mercury absorbed from the VaporPhase”; and Skrodas et al., Desalination (2007), 210(1-3), 281-286,“Role of activated carbon structural properties and surface chemistry inmercury adsorption.”

Sorbents in liquid systems typically include those with ionic groups tocapture materials in solution. The ionic groups may be inherent in thesorbent material, or added through a treatment of another sorbent suchas activated carbon. Materials such as amines and polyamines have beenstudied for use in removing metal ions. Polyamines are organic compoundsthat contain two or more primary amino groups. Polyamines generally havecations that are found at regularly-spaced intervals (unlike, say, Mg⁺⁺or Ca⁺⁺, which are point charges).

Amines reacted with activated carbon have been studied for use inpurifying water. Akio Sasaki, in U.S. Pat. No. 4,305,827, also teachesan adsorbent, obtained by reacting active carbon with a water-solubleamine and carbon disulfide, in the presence of water. The adsorbent isuseful in removing heavy metals, especially mercury, silver, gold,copper, and cadmium from water. The preferred amines are divalent orpolyvalent amines, including aromatic amines and poly(ethyleneimine).The adsorbents hold their adsorptive function well after being washed.Sasaki proposes that the amines react on the surface of the activatedcarbon; however, recently, there is some question that this occurs.

Sasaki, et al. studied a sorbent formed by reacting polyamines with CS₂in water, in the presence of palm-shell activated charcoal for used inremoving Hg⁺² ions in water. [See Sasaki, Akio, Kimura Yohiharu, NipponKagaku Kashi, 12, 880-886, (1997), “Preparation ofpolythiourea-immobilized activated charcoal and its utilization forselective adsorption of mercury(II) ion. Studies on functionalization ofpolymers by reactive processing. Part 5.”]. A Sasaki et al. propose thatthe secondary amine groups in the polymer backbone react with carbondisulfide to form thiourea crosslinked sites [e.g., >N—C(S)—N<].

Amine-containing polymers have been studied as sorbent materials fortreatment of water. Some amine-containing polymers can be derived fromnatural sources. For example chitosan, is a de-acylated derivative ofchitin, a glucosamine polysaccharide, is found in the shells of crabs,lobsters, and beetles. Chitosan has been used to absorb heavy metalsfrom water and industrial waste streams. [See Hawley's CondensedChemical Dictionary, 11^(th) edition (1987).]

Masari, et al., in U.S. Pat. No. 4,125,708, describes the use ofchitosan, modified with an anionic agent and glutaraldehyde, forremoving superoxy-anion-forming ions, such chromium. The anionic agentis selected from sulfite, sulfate, chloride, hexafluoride, and borategroups. The glutaraldehyde serves as a crosslinking agent. Othercrosslinking agents taught are glyoxal, glutaraldehyde, and dialdehydestarch. The crosslinked, anionically modified, nitrogen-containingproduct exhibits increased stability and insolubility over thenon-crosslinked product. Masari et al. teach that such sorbents could beused by adding a filter to an already-existing industrial or municipalwater purification system.

For mercury removal, use of a sulfur cure system would be attractive forpolymer-carbon sorbents used in mercury removal because sulfur has anaffinity for mercury. Sulfur vulcanization of polymers is used as aconventional curing system for strength and shelf life of rubber. Inaddition, sulfur vulcanization technology allows for a range ofvulcanization speeds and elastomer properties. In vulcanization ofpoly(isoprene) rubber, for example, sulfur forms a bond at points ofunsaturation in the polymer, and forms crosslinks between the polymerchains. In these cases, the elastomer molecules must contain allylichydrogen atoms. For additional information on curing systems see, forexample, The Science and Technology of Rubber, (1978), edited byFrederick R. Eirich, Academic Press, New York, “Vulcanization” by A. Y.Coran, pp 291-338.

Sulfur vulcanization is usually performed with an accelerator to controlthe cure time and characteristics. Accelerators include a number ofsulfur-containing compounds, plus a few non-sulfur types, such as ureas,guanidines, and aldehydeamines. Accelerated sulfur vulcanization hasbeen extended to other diene synthetic rubbers, such as SBR, butyl andnitrile rubbers. Accelerators that do not decompose or react witholefins at curing temperatures require an activator selected from basicmetallic oxides or salts of lead, calcium, zinc, or magnesium. Someaccelerators such as zinc salts of mercaptobenzothiazole and thedithiocarbamic acids do not require an additional activator. [See, forexample, Textbook of Polymer Science, 2^(nd) Ed., Fred W. Billmeyer.]

Also the continuous rise of the atmospheric carbon dioxide concentrationand its link with climate change demand a technological solution. Thissolution is especially needed for industries where large amounts ofcarbon dioxide result from burning operations, such as utility companieswhere coal is the fuel source. Carbon capture and sequestration toreduce such emissions have been considered for such mitigation. However,many industries use an amine-scrubbing technique as their solution;however, these methods cost can be very high. [See for example, R. S.Haszeldine, Science 325, 1647-1652 (2009).] Recently carbon-basedsupport materials, such as PEI on carbon materials, have become ofinterest. [See, for example, D. Wang et al., Energy Fuels 25, 456-458(2011).]

Therefore, a better system of polymer-carbon sorbents suitable forremoving carbon dioxide, toxic materials and heavy metals from flue gasthat is economical to run, especially on a commercial scale, is needed.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a polymer-carbon sorbent suitable forremoving one or more of carbon dioxide, heavy metal species or toxicmaterials from a flue gas from a combustion process, the sorbentcomprising a carbonaceous sorbent material and a cured amine-containingpolymer. Specifically, a process for preparing a polymer-carbon sorbentfor removing at least one of carbon dioxide, heavy metal species ortoxic materials from a flue gas from a combustion process fromcoal-fired power plants which sorbent comprises mixing and curing:

-   -   a) a carbonaceous sorbent material, and    -   b) a curable amine-containing polymer, comprising contacting an        amine-containing polymer having primary amine groups with an        allyl halide, in the presence of a catalyst, to form a curable        amine-containing polymer, comprising allyl end-groups, and        secondary and tertiary amine groups,    -   c) a sulfur agent, S₈ in its orthorhombic, monoclinic, or        amorphous, forms,    -   d) a cure accelerator, and    -   e) optionally, an activator.

In one particular embodiment, the polymer-carbon sorbent providesremoval of both elemental and ionic forms of metals, including mercury.In another embodiment, the polymer-carbon sorbent provides removal ofcarbon dioxide.

One aspect of this invention is a polymer-carbon sorbent for removingheavy metals from flue gas streams. The sorbent comprises a carbonaceoussorbent material and a cured amine-containing polymer, and sulfur. Theratio by weight of the carbonaceous sorbent material to curedamine-containing polymer can range from about 5:95 to about 95:5; andmore conveniently from about 50:100 to about 250:100. These ratiosdepend on the handling desired as well as the performance of thesorbent. Some sorbents of the invention are mixed and cured, followed bygrinding and/or selecting the sorbent to a desired size. Other sorbentsof the invention are formed by first creating a mixture of thecarbonaceous sorbent material, curable amine-containing polymer, sulfuragent, accelerator, and, optionally, an activator, then forming themixture into particles of a desired size and shape, and then curing theparticles.

The sorbents of this invention are formed by curing a curableamine-containing curable polymer in the presence of a carbonaceoussorbent material, sulfur, a cure accelerator and, optionally, a cureactivator. A convenient carbonaceous sorbent material is an activatedcarbon, and a convenient curable amine-containing polymer is an allylcontaining poly(ethyleneimine) having a number average molecular weightbetween about 1,000 and about 10,000. Sulfur in a range of about 5 toabout 60 parts per 100 parts by weight of polymer provides extensivecrosslinking and good mercury (Hg⁰, Hg₂ ⁺² and Hg⁺²) removal from bothgas and liquid systems. Preferably, the sulfur agent is in molar excessto the curable amine-containing polymer with the assumption that 10,000g of the polymer is 1 mole and 32 g of sulfur agent is 1 mole.

Another aspect of this invention is providing an allyl group to anamine-containing polymer to form a curable amine-containing polymer.Preferably, the amine-containing polymer has both primary and secondaryamine groups. A convenient source of an allyl group is an allyl halide,such as allyl bromide or allyl iodide. The allyl halide andamine-containing polymer react so that allyl groups replace primaryamine groups at the chain termini on the amine-containing polymer. Forcarbon dioxide removal, the amine-containing polymer preferably hasmultiple available amine groups on the surface, such aspoly(ethyleneimine) with allyl groups.

Another aspect of this invention is a method of removing vaporized metalspecies, especially mercury in the forms Hg⁰, Hg₂ ⁺², and Hg⁺², fromflue gas of a combustion process by contacting the flue gas with anadsorbent for a sufficient time to remove the metal species, and thenremoving the adsorbent before exhausting to the air. The sorbent iscapable of removing both elemental and oxidized forms of the metalspecies.

A further aspect of this invention is removal of carbon dioxide from theflue gas stream by use of amine-containing polymers having secondary,tertiary and primary amine groups that adsorb carbon dioxide readily.The present polymer-carbon sorbent provides that amine availability. Oneexample of such a present polymer-carbon sorbent that is advantageouscontains poly(ethyleneimine) with allyl groups and carbon black in asulfur crosslinked form. This sorbent can be used alone or with theroutinely used carbon black in flue gas of coal-fired power plants.While carbon black alone adsorbs only mercury and mercury ions, thepresent polymer-carbon sorbents adsorb carbon dioxide and chemicallybind mercury and mercury ions. Thus the present polymer-carbon sorbentshave dual acting properties and are cost effective. The presentpolymer-carbon sorbents contain primarily secondary and tertiary aminenitrogen atoms and lack primary amine groups due to the modificationsdescribed above. The secondary and tertiary nitrogen amines are moreelectron rich than the primary amines which are inherent in PEI.Therefore it is expected that the present polymer-carbon sorbents willadsorb more carbon dioxide than PEI impregnated on carbon black.Furthermore, the in modified polymer-carbon sorbent described herein PEIis crosslinked. This crosslinking should prevent dissolution of PEI bythe moisture present in the flue gas, unlike the materials described byWang et al. The same investigators have reported degradation of theirmaterial in flue gas. In contrast, current studies indicate the oppositefor the present polymer-carbon sorbent; the present polymer-carbonsorbent reported herein can withstand the flue gas environment for aconsiderable length of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A schematic of a system for injecting sorbent into a flue gasstream, prior to a filter

FIG. 2 A schematic of a system for injection sorbent into a flue gasstream, prior to an electrostatic precipitator (ESP)

FIG. 3 A schematic of a system for injecting sorbent into a flue gasstream after an ESP

FIG. 4 A schematic of a system for injecting sorbent into a flue gasstream before a spray dryer

FIG. 5 FIG. 5 a shows Steps 1-3 and FIG. 5 b shows Steps 4 and 5 of areaction to form an allyl-capped poly(ethyleneimine) (ACP) withcrosslinking of the ACP with sulfur and zinc diethyldithiocarbamate

FIG. 6 Schematic of equipment setup for testing elemental mercuryadsorption

FIG. 7 Capture of elemental mercury in mg Hg⁰ by parts weight sulfurused for polymer-carbon sorbent

FIG. 8 Capture of ionic mercury in mg Hg⁺² by parts weigh sulfur usedfor polymer-carbon sorbent

DESCRIPTION OF INVENTION Glossary

The following terms as used in this application are to be defined asstated below and for these terms, the singular includes the plural.

ACP means allyl-capped polymer

BPEI means branched poly(ethyleneimine)

CAC means FLUEPAC®—MC Plus

DH means DARCO® Hg, an activated carbon

DHL means DARCO® Hg-LH, an activated carbon

DMAC means dimethylacetamide

DSC means differential scanning calorimetry

DTC means dithiocarbamate

ESP means electrostatic precipitator

MAC means modified activated carbon

PAC means powdered activated carbon

TGA means thermogravimetric analyses

ZnDEDC means zinc diethyldithiocarbomate

Discussion

The present invention provides a polymer-carbon sorbent suitable forremoving heavy metal species from flue gas systems, such as found incoal-fired power plants, the sorbent comprising a carbonaceous sorbentmaterial and a cured amine-containing polymer. Specifically, apolymer-carbon sorbent for removing carbon dioxide, heavy metal speciesand toxic materials from a flue gas from a combustion process whichsorbent comprises:

-   -   a) a carbonaceous sorbent material, and    -   b) a cured amine-containing polymer wherein        -   i) a sulfur agent, used to cure the curable amine-containing            polymer, is selected from allotropes of elemental sulfur,            which is added in molar excess of the amount required to            cure the curable amine-containing polymer, in the presence            of a carbonaceous sorbent material, and        -   ii) the curable amine-containing polymer is formed by            reacting an amine-containing polymer with an allyl halide.

These present polymer-carbon sorbents that are suitable for removingheavy metal species from a flue gas are especially useful for removal ofheavy metals from power plants. Coal comes in four grades; anthracite,bituminous, sub-bituminous, and lignite. Anthracite produces the highestheat energy per unit weight. It is expensive which prohibits its use inpower plant boilers. Bituminous coal provides lesser heat per unitweight than anthracite and has higher chlorine content, which allows forthe conversion of elemental mercury to its water-soluble ionic (toxic)forms. Most bituminous coal has been exhausted in the Americas. Thus,sub-bituminous coal and lignite are the two types of coal that are usedin power plant operation. Besides their lower heat content, they havelower chlorine content. Thus, during combustion, more elemental mercuryis produced. For these latter two types of coal, the chlorine contentscan vary widely depending on its source. Therefore it is desirable todesign a sorbent with tunable elemental mercury absorbing capacities.The present sorbent can be tailored to meet these demands. This isachieved by changing the ratio of cured amine-containing polymer and acarbonaceous sorbent material such as activated carbon. By increasingthe carbon to polymer ratio, while keeping other parameters constant(S:45 parts, etc.), the mercury absorbing capacity can be decreasegradually to reach that of the lower level achieved by DARCO®—Hg-LHalone. Thus, mercury chemisorption capacity is tunable; increasingcarbon content relative to the amine containing polymer systematicallylowers elemental mercury loading capacity accordingly.

Amines with activated carbon, and particularly cured amine-containingpolymers, have not been described for use in gaseous in-flight removalof mercury. A cured amine-containing polymer could improve capture ofmetals and their ions in gas treatment systems. For types of treatmentsystems in order to use a polymer-carbon sorbent, it would be convenientto have a polymer that has been crosslinked, to improve the handling andstability of the polymer-carbon sorbent. However, curable syntheticamine polymers with conventional curing systems have not been reportedfor use in removing metal ions from gases.

The present invention uses mixing and curing a carbonaceous sorbent anda curable amine-containing polymer in the presence of a sulfur agent, acure accelerator, and optionally an activator, provides a noveladsorbent for use in removing heavy metal species, especially metallicmercury and mercury ions, from flue gas streams. Laboratory screeningindicates that the resulting polymer-carbon sorbent has higher capacityfor both elemental and ionic species of mercury than that of acommercially available carbon sorbent alone.

The ratio by weight of the carbonaceous sorbent material and curedamine-containing polymer can range from about 2:1, or a range of about5:95 to about 95:5, more conveniently from about 50:100 to about250:100. A sorbent of the invention can be mixed and cured, followed bygrinding, or otherwise reducing particles of the sorbent to a desiredsize. For example, for use in sorbent injection systems, particles canbe ground to an average particle size of less than about 100 μm, orpreferably about 50 μm. A convenient range of a ratio of carbonaceoussorbent material to cured amine-containing polymer in this use is about60:40 to about 95:5. A more convenient range of ratio of carbonaceoussorbent material to cured amine-containing polymer is about 50:100 to250:100.

Other sorbents of the invention are formed by first creating a mixtureof the carbonaceous sorbent material, curable amine-containing polymer,sulfur agent, accelerator, and, optionally, an activator, then formingthe mixture into particles of a desired size and shape, and then curingthe particles. For these sorbents, a convenient range of a ratio byweight of the carbonaceous sorbent material and cured amine-containingpolymer, such as to hold a shape, would be from about 5:95 to about30:70. A more convenient ratio by weight of the carbonaceous sorbentmaterial and cured amine-containing polymer would be from about 5:100 toabout 50:100 parts by weight. These ratios will depend on the lowerlimit of carbon that must be present to get a curable mixture. Theamount and molecular weight of curable amine containing polymer affectsprocessing to form shapes by, for example, spraying fine particles,extrusion, or molding. Adsorbents that are larger in size may be moreuseful in fixed bed filters or columns Convenient sizes foe use inliquid systems typically range from about 100 nm to as large as about 5mm in the longest dimension.

The carbonaceous sorbent materials of this invention are selected fromactivated carbon, treated activated carbon, powdered activated carbon,activated charcoal, activated coke, char, incompletely burned carbonfrom a combustion process, crumb rubber of appropriate mesh size(400-450) or carbon black. Convenient sources of carbonaceous sorbentmaterials are commercially available activated carbons and treatedactivated carbons. Even more convenient are activated carbons that aretreated on the surface for use in removing contaminants from flue gasstreams. Such treatments may include sulfur or bromine, for example, toenhance adsorption of mercury. Examples of such treated activatedcarbons include FLUEPAC®-ST and FLUEPAC®-MC Plus, from Calgon CarbonCorporation, Pittsburgh Pa., and DARCO® Hg and DARCO® Hg-LH, from NoritAmericas Inc., Marshall Tex. These treated activated carbon products areprovided as powders.

The curable amine-containing polymers of this invention are formed bymodifying an amine-containing polymer with an allylic compound to formallyl end-groups. Suitable amine-containing polymers contain primaryand/or secondary amine groups along its chain and end-groups, or onpendent groups along the chain. Such amine-containing polymers includepoly(p-aminostyrene), poly(allylamines), poly(aniline), poly(vinylamine)and its copolymers, poly(ethyleneimine), chitosan, amine containingcopolymers, and the like.

An aspect of this invention is a method to add an allyl group to anamine-containing polymer by reacting amine end-groups on the polymer, oron pendant chains on the amine-containing polymer, with an allyl halideto form a curable amine-containing polymer of this invention. Additionof the allyl group takes place in the presence of a strong base, and asolvent, preferably a solvent with a relatively large dielectricconstant. Convenient allyl halides include allyl bromide or allyliodide. Convenient bases include potassium carbonate, and sodiumcarbonate. Convenient solvents include dimethylacetamide,N-methyl-pyrrolidinone, dimethyl sulfoxide and N,N-dimethylformamide.

An example of such a method is the reaction between branchedpoly(ethyleneimine) and allyl bromide that demonstrates the formation ofa curable amine-containing polymer. The allyl bromide reacts with amineend-groups on the poly(ethyleneimine), in the presence of potassiumcarbonate and a solvent with a relatively large dielectric group, suchas dimethylacetamide (DMAC), to form a polymer with (secondary) aminegroups in the chain and allyl end-groups. While not wishing to be boundby theory, it is believed that the potassium carbonate assists thereaction by reacting with HBr, the by-product of the reaction.

FIG. 5 gives a schematic representation of the reaction of allyl bromidewith a branched poly(alkyleneimine), in the presence of potassiumcarbonate, to form a curable amine-containing polymer of this invention.The poly(alkyleneimine) has pendant chains with primary aminoend-groups. A primary amine group on a poly(alkyleneimine) reacts withthe allyl radical from the allyl bromide. During the reaction, primaryamines in the polymers are converted to secondary amines, and terminalallyl end-groups are introduced into the polymer. The terminal allylend-groups are then available to facilitate crosslinking, so that theresult is a curable amine-containing polymer.

Secondary amines are less nucleophilic than primary amines. However, ifan excess of allyl bromide is available, some reaction between the allylbromide and secondary amines might occur.

The reaction to form curable amine-containing polymers of the presentinvention can take place using conventional chemical mixing equipment.For example, a stirred, jacketed reactor will be useful. When thereaction is exothermic, the jacket may be supplied with a cooling liquidto control temperatures. If a polymer is selected that is near 10,000Mw, equipment suitable for medium to high viscosity, such as double armmixer, planetary mixer, plastic extruder, or the like may be moreuseful. Again, cooling of the mixing equipment is useful to controltemperatures. (Suitable equipment manufacturers include B & P ProcessEquipment, Saginaw, Mich., and Charles Ross & Son Company, Hauppauge,N.Y.)

In an aspect of this invention, curable amine-containing polymers arevulcanized in the presence of a carbonaceous sorbent material to form apolymer-carbon sorbent. There are several general methods of vulcanizingpolymers having allyl groups. Examples of conventional methods forvulcanization of allyl groups, as discussed above in the background,include use of accelerated sulfur vulcanization, peroxide catalysts, andchain extension. Sulfur vulcanization has the advantage of providingadditional sulfur to the polymer-carbon sorbent, beyond any that mayalready be present on the carbonaceous sorbent material. A sulfur agentis used for vulcanization in this invention. A sulfur agent is S₈, whichmay be in orthorhombic, monoclinic, and amorphous forms. Preferably, thesulfur agent is added in an amount more than twice the amount requiredto cure the curable amine-containing polymer.

In one aspect of this invention, it has been found that sulfurvulcanization is useful for curing an allyl-capped poly(alkyleneimine)in the presence of activated carbon. Sulfur vulcanization of otherpolymers with allyl groups results in a polymer with sulfur cros slinks;the allyl groups remain in the polymer. For example, whenpoly(cis-1,4-isoprene) rubber is crosslinked using elemental sulfur,sulfide bridges are introduced between chains of the polymer. In anotheraspect of this invention, sulfur vulcanization is useful when curingpoly(alkyleneimine) in the presence of an activated carbon that istreated with bromine.

While not wishing to be bound by theory, it is believed that the sulfurused in the vulcanization provides additional chemical binding of someheavy metal species. For example, sulfur reacts readily with mercury toform HgS, which is found as cinnabar in nature. Thus if HgS can be madeas a product of this present process, it is environmentally preferred.

Use of an accelerator with sulfur vulcanization allows control of thecuring time, temperature, and the properties of the resulting curedamine-containing polymer. An accelerator can be selected from any of thetraditional accelerators used in sulfur vulcanization. Accelerators usedin sulfur vulcanization include a number of sulfur-containing compounds,such as thioureas, thiophenols, mercaptans, dithiocarbamates, xanthates,trithiocarbamates, ditihio acids, mercaptothiazoles,mercaptobenzothiazoles, and thiuram sulfides, plus a few non-sulfurtypes, such as ureas, guanidines, and aldehydeamines.

Optionally, an activator is used to start the vulcanization reaction.Accelerators that do not decompose or react with olefins at curingtemperatures require an activator selected from basic metallic oxides orsalts of lead, calcium, zinc, or magnesium. However, some acceleratorssuch as zinc salts of mercaptobenzothiazole and the dithiocarbamic acidsdo not require an additional activator, and may be more convenient. Inthe present invention, an activator is optional, and required only ifsuch a zinc salt is not used.

An example of such a convenient accelerator is zincdiethyldithiocarbamate (ZnEDC). While not wishing to be bound by theory,FIG. 5 depicts sulfur vulcanization of a polymer containing an allylgroup, using ZnEDC. In Step 1, the ZnEDC initiates the reaction byundergoing hemolytic cleavage to form two identical radicals. In Step 2,two of these radicals then come together to open the sulfur ring, toform a polysulfide chain. In Step 3 the reaction proceeds by abstractionof an allylic hydrogen, followed by rearrangement of the double bond. InStep 4, the other accelerator moiety is eliminated via hemolyticcleavage, leaving a terminal radical on the polysulfide group. In Step 5the terminal radical attacks the alpha carbon on a second allyl group,resulting in a crosslinked polymer. The crosslink that is formed is apolysulfide bridge, and the double bonds remain in the polymer, some ofwhich can also interact with S₈ to form cyclic polysulfides.

The cure time and temperature for vulcanization is dependent on theaccelerator and activator used for curing. It is convenient if the curetemperature is well below the decomposition temperature of theamine-containing curable polymer. The decomposition temperature can bedetermined by standard techniques, such as TGA. (It should be noted thatthe cure is exothermic as heat is needed to form the initiator species,as evidenced by DSC.)

The polymer-carbon sorbent of this invention can be cured with sulfurvulcanization; as one such example, with 7 parts sulfur in 100 partsamine-containing curable polymer, with 200 parts bromine-treatedactivated carbon and 1 part zinc diethyldithiocarbamate accelerator.Curing for this example recipe can take place at about 111° C. for about30 minutes.

The polymer-carbon sorbents of this invention are made by conventionalmethods for compounding polymers with particles and curing agents. Whenthe curable amine-containing polymer and carbonaceous sorbent materialare both in solid form, they can be ground together with sulfur,accelerator and optional activator. Alternatively, a solvent can be usedto dissolve polymer and suspend solid ingredients, including thecarbonaceous sorbent material.

The type of equipment used to mix the uncured polymer-carbon sorbentswill depend on any solvents that are used, the viscosity of curableamine-containing polymer in solution, the loading of carbonaceoussorbent material, the expected cure rate, and whether the process is tobe batch or continuous. For extremely high viscosity mixtures, planetarymixers, extruders, roll mills, and the like may be needed to combine thecarbonaceous sorbent material with the curable amine-containing polymer.(Manufacturers of suitable equipment include, for example, B & P ProcessEquipment, Saginaw, Mich., and Charles Ross & Son Company, Hauppauge,N.Y. and other manufacturers.)

The equipment should provide for heating or cooling of the ingredients,depending on whether the vulcanization reaction is endothermic orexothermic, respectively. The temperature during mixing ofamine-containing curable polymer and carbonaceous sorbent material willdepend on the temperature required by the accelerator and optionalactivator. If the ingredients are mixed before curing, it is convenientto maintain the temperature several degrees below the cure temperature.For many accelerators, it is convenient if the temperature is maintainedat about 25° C. or below. Curable amine-containing polymer, carbonaceoussorbent material, sulfur, accelerator and activator may be mixed in abatch mixer, without heating, and then transferred to a heated press ormold for curing. Alternatively, the ingredients may be added to acontinuous process such as an extruder or tank, and then heated afterextrusion or spraying to form cured particles. When fully cured, thepolymer-carbon sorbents of this invention possess similar or superiorthermal stability so that they can be used to replace activated carbonto treat flue gasses or chemical process wastes.

In another aspect of this invention, it was found that it is necessaryto cure the curable amine-containing polymer in the presence of aneffective amount of carbonaceous sorbent material. In addition to actingas a sorbent, the carbonaceous sorbent material acts as a reinforcementmaterial and as a filler.

For a particular combination of polymer and carbon, a sulfur saturationpoint can be determined by examining the polymer-carbon solvent for freesulfur, for example, testing the sample by DSC before and after a curestep. To determine saturation for a given polymer, polymer-carbonsorbent samples with increasing amounts of sulfur can be cured andcompared. Before saturation, the presence of peaks in a DSC thermogram,corresponding to the melting points of sulfur S₈ allotropes at 112° C.and 119° C., disappear when the polymer is cured. After saturation, thepeaks at 112° C. and 119° C. remain, even after the polymer is cured,indicating free sulfur is available.

In yet another aspect of this invention, polymer-carbon sorbents aretreated with 2-mercaptoethanol to introduce thiol moieties into thesamples. For example, polymer-carbon sorbents may be treated with2-mercaptoethanol, which reacts with a disulfide crosslink in thepolymer-carbon sorbent by cleaving the disulfide bonds. Thiols have ahigh affinity for Hg⁰ as well Hg⁺². Therefore, adding thiol groups to apolymer-carbon sorbent can increase overall mercury capture.

Another aspect of this invention is a method of removing vaporized metalspecies, especially mercury in the forms of Hg⁰, Hg₂ ⁺², and Hg⁺², fromflue gas of a combustion process by contacting the flue gas with anadsorbent for sufficient time to remove the metal species and thenremoving the adsorbent before exhausting to the air. The sorbent iscapable of removing both elemental and oxidized forms of the metalspecies. In particular, it is an aspect of this invention to provide amethod to use polymer-carbon sorbents to remove vaporized metals andmetal ions from combustion streams by injecting a polymer-carbon sorbentinto the flue gases, as described above. Any of the equipment for orvariations to injection systems known in the art, such as electrostaticprecipitators, bag filters, and others, may be useful to remove thepolymer-carbon sorbent before the flue gasses exit the system. Theeffectiveness or working life of the polymer-carbon sorbent may beextended by taking advantage of other systems for sulfur or NO_(x) toremove other contaminants from the system. The present polymer-carbonsorbent is able to absorption of elemental mercury capacity of aboutthree times that of DLH, with fewer injections into the flue gas and/orhas a longer residence time.

A particularly convenient approach for injection of a polymer-carbonsorbent to flue gases includes a TOXECON® arrangement, as shown in FIG.3. In such an arrangement, fly ash and other solids are removed beforethe injection of a polymer-carbon sorbent. Such a process allowsrecovered fly ash to be sold as a by-product and the polymer-carbonsorbent to be captured for regeneration or for reuse as a source ofmercury. This process is of limited utility, because, complete removalof particulate mercury from fly ash is not feasible. Theadsorption-desorption of mercury from the adsorbent does not guaranteecomplete removal of adsorbed species.

In order to be useful in an injection system, the particles of thepolymer-carbon sorbent must be kept in suspension in the flue gas untilit reaches a filter or ESP for collection. Typically this means that theparticles are kept small and have surface properties that do not promoteclumping. In addition, particles that are captured in a filter need toallow continued gas flow without causing a large pressure drop. Usefulparticles are less than about 100 μm, and more conveniently less thanabout 50 μm.

Yet another aspect of this invention is removal of heavy metal species,such as arsenic, cadmium, cesium, copper, gold, iron, lead, mercury,palladium, platinum, plutonium, selenium, silver, strontium, thallium,uranium or mixtures thereof from mining or industrial wastewaterstreams. Removal of toxic materials, such as the heavy metal species ofperchlorate or arsenate, that have the polymer-carbon sorbent furthermodified with appropriate modifications to an existing system can alsobe a use of the present sorbents.

When a fluid, such as flue gas containing water or liquids, is to betreated with the present sorbents, then the absorbent media can beformed into beads, pellets, filter, film, and others for use. Themixture is formed into the adsorbent media and then cured. The presentpolymer-carbon sorbent may be used in conventional ways for such fluids,such as fixed beds, columns, or other means, whereby that heavy metal iscontacted with the sorbent as the fluid passes and, if desired, thesorbent can be extracted and the polymer-carbon sorbent regenerated.Typical methods are used to recycle the gas as needed over the sorbent.

In most methods for using the polymer-carbon sorbents of this invention,it may be useful to contact a fluid stream, such as flue gas, with thesorbent more than once to remove additional heavy metal species. Whenextra treatment is desired, a recycle loop can be added to a fluidtreatment system. For example, referring to FIG. 3, a recycle loop woulddivert stream 63 to re-enter the flue gas stream 67, ahead of sorbentinjection site 71. Similarly, in a fixed bed or column, a recycle may berun from the exit of the fixed bed or column to the entrance.

In another aspect of this invention, the polymer-carbon sorbents of thisinvention can be used to treat solid waste that contains mercury. Solidwaste is treated with a solvent or caustic and/or acidic solutioncapable of dissolving mercury species. The solution is then treated bycontacting it with a polymer-carbon sorbent to remove mercury in itselemental or ionic form. It should be pointed out that the existing andhighly prevalent method of oxidizing elemental mercury to ionic formonly renders it water-soluble. This enables water-soluble mercuryspecies to enter the water stream. The subsequent fate of these salts isunknown.

In another aspect of this invention, polymer-carbon sorbents that areused to collect mercury species can be further treated to reclaim themercury and recycle the sorbent.

While not wishing to be bound by theory, it is believed that all of theelemental mercury on the polymer-carbon sorbent is present as HgS(cinnabar). Experimental findings strongly suggest that the ionicmercury species are bound to the polymer-sorbent by strong co-ordinationwith nitrogen atoms present in the polymer-sorbent. Mercury as a metalis valuable, and methods for recovering mercury or cinnabar from wastestreams are known in the art and may prove useful here.

EXAMPLES

The following examples are presented to clarify, but not limit, thescope of the invention.

Materials

With the exception of activated carbon, all reactants and solvents werepurchased from Aldrich Chemical Company, Milwaukee, Wis. Branchedpoly(ethylenimine)s (BPEI) having nominal number-average molecularweights (Mn) of about 10,000, 2,000 and 1,300, zincdiethyldithiocarbomate (ZnDEDC), orthorhombic sulfur, toluene andmethanol were used as purchased. Allyl bromide was distilled prior touse. Dimethylacetamide (DMAC) was distilled over calcium hydride atreduced pressure.

Three activated carbons commercially used in flue gas treatment, (CAS#7440-44-0) were tested to compare with the sorbents of the invention.One activated carbon FLUEPAC®-MC Plus (CAS #7440-44-0) from CalgonCarbon Corporation, Pittsburgh, Pa. (CAC), and DARCO® Hg (DH) and DARCO®Hg-LH (DHL) from Norit Americas Inc., Marshall, Tex. The activatedcarbon tested in polymer-carbon sorbents of the invention was DARCO®Hg-LH Powdered Activated Carbon from Norit Americas, Inc., Marshall,Tex., an impregnated lignite coal-based activated carbon. DARCO® Hg-LH,abbreviated DHL, was used to make the polymer-carbon sorbent in theexamples; DHL has a proprietary bromine treatment specifically forremoval of mercury from flue gas emissions from burning low halogenfuels. It has and average sulfur content of 1.2 weight percent. (NoritActivated Carbon Datasheet No. 1121, June 2007, Norit Americas, Inc.)

Celite® diatomaceous earth, Mallinkrodt Baker Inc, Phillipsburg, N.J.was used as a filter media to purify products.

Measurements

Thermogravimetric analyses (TGAs) were performed using a TA Instruments2590 Hi-Res TGA with a flowing nitrogen atmosphere. Differentialscanning calorimetry (DSC) measurements were conducted using a TAInstrument 2910 Modulated DSC with a heating rate of 5° C./min

Infrared (IR) spectra were obtained using a Nicolet 20DXB FourierTransform Infrared Spectrometer. Samples were prepared by placing a thinlayer of an analyte in solution on a salt plate (NaCl) and then allowingthe solvent to evaporate.

H-1 and Carbon-13 NMR spectra were obtained on a Varian Mercury-Plus 300MHz Spectrometer, and the chemical shifts are reported in ppm withtetramethylsilane as the internal standard. Samples were prepared indeuterated trichloromethane.

Inductively Coupled Plasma Mass Spectrometer (ICP-MS) measurements wererecorded on a Fisons Plasmaquad II+ICPMS. Samples were diluted asrequired.

Mixtures of activated carbon, BPEI, sulfur and ZnDEDC were cured on aPHI High Temperature Smart Press at 130° C. for 25 minutes.

Elemental Mercury Capture FIG. 6 shows a schematic representation ofreaction vessel for testing the efficiency of elemental mercury captureby MAC samples. A clean, dry, Petri dish (60×15 mm) 84 was weighed, andthe weight was recorded. In order to prevent mercury deposition, theexternal surface of the Petri dish was then wrapped with Parafilm® Msealing film [BRAND GMBH and CO KG, Wertheim (Germany)] a stretchable,chemical resistant self-sealing film. The bottom of the Petri dish 84was evenly covered with the adsorbent samples (2 g). The dish wassuspended in the mercury chamber 85 containing about 10 mL of liquidmercury. The mercury chamber 85 was heated using an external oil bath86. The oil bath temperature was raised to 140° C., and held at thattemperature using a temperature controller. The bath temperaturemaintained the chamber temperature surrounding the suspended Petri dishat about 100° C. as read on a thermometer 83. An air condenser 87, glasstube 88, iodine chamber 89 and drying tube 90 were used to trap anymercury vapor escaping and prevent moisture from entering into thereaction chamber. The dish was left in the chamber for 24 hours. The oilbath 86 was removed and the mercury chamber 85 was allowed to cool toroom temperature. The Petri dish 84 was removed from the chamber and theParafilm® was removed. The weight of the Petri dish containing MAC wasrecorded, then the Parafilm® was removed and the dish and sample wereweighed.

COMPARATIVE EXAMPLE A Testing Commercial, Activated Carbon Samples forHg⁰ Capture

Using the method described above in the measurements section, efficaciesof three commercially available activated carbon samples were tested toselect the activated carbon with the highest capture of Hg⁰. Findingsfrom testing CAC, DH, and DHL are summarized in Table 1 below. The DHLhad a higher affinity for capturing elemental mercury in our testmethod. DHL was then selected to use in polymer-carbon sorbents.

TABLE 1 Capture of Elemental Mercury for Commercial Activated Carbon inmg Hg⁰ per gram Activated Carbon Activate Carbon Trial 1 Trial 2 Trial 3Average CAC 51 60 46 52 DH 32 29 29 30 DHL 73 64 75 71

EXAMPLE 1 Preparation of Curable Amine-Containing Polymers

Three different poly(ethyleneimines)s, (BPEIs), having nominal numberaverage molecular weights of 1300, 2000, and 10,000 were selected asamine-containing polymers. They were each allowed to react with allylbromide to form allyl-capped poly(ethyleneimine), ACP, as the curableamine-containing polymers.

The procedure for the 10,000 Mn follows as an example: 5.0 g (˜0.0005mole) was weighed into a 150 mL beaker, and DMAC (50 mL) was added tothe beaker, while stirring using a magnetic stir bar, to prepare a clearsolution. A four-necked, round-bottomed flask, fitted with an overheadstirrer, nitrogen inlet, thermometer, and an addition funnel served asthe reaction vessel. The BPEI solution was added to the reaction vessel.The beaker containing the polymer solution was washed with additional 20mL of DMAC and the washing was added to the reaction vessel, followed byabout 5.0 g (about 0.036 mol) anhydrous potassium carbonate about 5.0 g,excess). Allyl bromide (25 mL, about 0.148 mol) was transferred to adropping funnel, and then added drop-wise over a ten-minute period tothe reaction vessel, while the reaction was allowed to continue withstirring. An initial exotherm of about 40° C. was observed and the colorof the reaction mixture turned light orange. The reaction was allowed tocontinue at room temperature for about 10 hours under a constant purgeof nitrogen, also at room temperature. The reaction vessel was protectedfrom external light sources during the reaction by covering it withaluminum foil. This was done to protect the newly-formed allyl groups onthe polymer from light-induced polymerization.

At the completion of the reaction, excess DMAC was decanted from aDMAC-swollen reaction product. To remove salts (particles of excesspotassium carbonate, potassium bromide), the DMAC-swollen reactionproduct was dissolved in 50 mL of methanol and filtered through Celite®diatomaceous earth, to form a filtrate containing allyl-cappedpoly(ethyleneimine) (ACP). Then, the filtrate was added drop-wise intorapidly stirring anhydrous diethyl ether. The ACP in the filtrate wasnot soluble, and precipitated out of the diethyl ether, and it wasfiltered. The residue was re-dissolved in methanol and the solution wastransferred to a 500 mL round-bottomed flask. The methanol, along withany residual ether, was removed from the ACP using a rotary evaporatorat reduced pressure. The flask, covered with aluminum foil, was dried ina vacuum oven at room temperature for an additional 12 hours to removeany residual diethyl ether or methanol, producing a dried and purifiedACP. The dried, purified ACP, as a flaky orange solid, was removed fromthe flask and stored in a brown vial at −20° C.

Characterization of ACP from BPEI having a Nominal Mn of 10,000

H-1 NMR spectra of a BPEI starting material and product ACP wereobtained. The H-1 absorbances of the BPEI were localized between 2.5 and2.8 ppm. The absorbances in the H-1 spectrum of ACP were dispersed overa range from 2.5 to 6.5 ppm, and shifted downfield from the absorbancesof BPEI. On the ACP spectra, the set of absorbances between 5.0 and 6.5ppm can be attributed to hydrogen nuclei attached to sp² hybridizedcarbons. The absorbances localized between 4.0 and 4.8 ppm correspond tohydrogen nuclei attached to secondary amines. The absorbances from 2.5to 4.0 can be attributed to hydrogen nuclei attached to sp³-hybridizedcarbons. The downfield shift of the absorbances observed in the ACPspectrum, especially the shift attributed to hydrogen atoms attached tothe sp³ hybridized nuclei, can possibly be explained by long-rangethrough-space interactions.

Infrared spectroscopy (IR) was performed to confirm the addition of anallyl group to BPEI samples. The IR spectrum was taken of ACP, formedfrom BPEI having a nominal Mn of 10,000, showed absorbance at 3380 cm⁻¹due to N-H stretching. The absorbances at 2955 cm⁻¹, 2527 cm⁻¹, and 1449cm⁻¹ are due to sp³hybridized C-H stretches. The presence of the alkeneis evident at the absorbance at 1629 cm⁻¹ corresponding to acarbon-carbon double bond. Furthermore, the absorbances centered at 3100cm⁻¹, 990 cm⁻¹, and 927⁻¹ correspond to the C-H deformations of aterminal sp² hybridized carbon. These are consistent with the additionof the allyl group to the primary amine of the poly(ethyleneimine).

In addition, comparing the ACP with IR spectra of a BPEI having anominal Mn of 10,000, the ACP lacked a primary amine absorbance at 1588cm⁻¹, which was present in the BPEI. The loss of this peak is consistentwith primary amine groups from BPEI being consumed in the reaction. Therelative intensity of the absorbance at 3277 cm⁻¹ in BPEI was reduced inthe ACP, which is also consistent with loss of the primary amine groups.

Thermal Gravimetric Analysis (TGA) was used to determine decompositiontemperature of ACP samples. An ACP made from a BPEI having a nominal Mnof 10,000 was found to start decomposing at about 158° C., leading toabout a 75% decrease in mass, until the temperature reached about 360°C.

TGA was also used to determine thermal stability of ACP at constanttemperature. An isothermal TGA thermogram was obtained at 130° C. for 60minutes for an ACP made from a BPEI having a nominal Mn 10,000. Thethermogram showed a mass loss of about 5.9%, probably due to the loss ofabsorbed moisture, similar to that of LGH.

COMPARATIVE EXAMPLE B

Vulcanization of a Curable Amine-Containing Polymer, ACP, without Carbon

Comparative Sample 1, ACP without any carbon, was prepared for cure inthe absence of activated carbon. A mixture was prepared using 100 partsACP, from a PEI having a Mn of about 10,000, 13 parts sulfur, and 1 partZnEDC. A DSC thermogram was obtained to determine the temperaturenecessary to carry out the crosslinking reaction. An examination of thethermogram showed the presence of sulfur melting endotherms at 115° C.and 119° C., but a cure endotherm was absent in the sample before cure.Despite this indication that the polymer might not cure, the mixturesample was placed in a press and heated at 115° C. for 15 minutes. Themixture turned to a dark brown sticky material, and then hardened andbecame a brittle material upon cooling. The brittle material dissolvedeasily in methanol at room temperature. This indicates that carbon isessential for the curing process.

EXAMPLE 2 Polymer-Carbon Sorbent Cure Temperature Study

DSC of uncured samples was used to determine a curing temperature forpolymer-carbon sorbents at different sulfur levels. The samples weremade from an ACP prepared from a PEI having a Mn of about 10,000.Thermograms from the DSC of uncured samples had broad endotherm curves,over a temperature range from 40 to 150° C. Endotherms of uncuredsamples had peaks ranging from 90 to 112° C., indicating curetemperature(s) for the samples.

Sample 2(a) was made using 100 parts ACP, 7 parts sulfur, 1 part ZnEDC,and 200 parts DHL. The DSC thermogram obtained prior to curing exhibiteda curing endotherm peak at 111° C., with an activation energy of 92.27J/g. After curing for 30 minutes at 111° C., an endotherm was notobserved, indicating the completion of the curing process.

Sample 2(b) was made with 100 parts ACP, 13 parts sulfur, 1 part ZnEDC,and 200 parts DHL. The sample was cured at 92° C. for 15 minutes.

Sample 2(c) was made with 100 parts ACP, 11 parts sulfur, 1 part ZnEDC,and 200 parts DHL. The pre-cure thermogram showed a peak at 103° C. andan activation energy of 148 J/g. After curing for 15 minutes at 103° C.,an endotherm with a peak at 84° C. and an activation energy of 31 J/kgwas evident. After curing an additional 15 minutes at 103° C., a minorendotherm was found with a peak at 105° C. and an energy of 49 J/kg.That is, the additional cure did not reduce the endotherm further. Thisappeared to indicate that the cure may have been completed, but thatother chemical processes may be contributing to the endotherm.

Based on the observations above, and to ensure curing was complete forall samples, a curing time of 25 minutes and a curing temperature of130° C. were chosen for further studies.

EXAMPLE 3 Preparation of Polymer-Carbon Sorbent with High Sulfur Content

The polymer-carbon sorbent samples were prepared from the samples of ACPprepared in Example 1, using the following general procedure. For thesesamples, 200 parts of DARCO® Hg-LH (DHL) and 100 parts of ACP were used.The amount of sulfur and that of ZnDEDC was varied, while keeping themass ratio of sulfur to ZnDEDC fixed at 5:1. For each molecular weight,samples were made using 30, 40, 45 and 50 parts by weight sulfur,respectively, for 100 parts by weight of the ACP. These amounts are inexcess of that required to show a cure of the polymer-carbon sorbentsused in Example 2. The mercury capture of the sorbent samples was thencompared to that of DHL.

As an example of the procedure, a sample preparation with 50 partssulfur and subsequent curing is as follows: ACP (5 g), sulfur (2.5 g),and ZnEDC (0.5 g) were weighed and transferred to an evaporation dishand grounded to powdery form using a pestle. That is, the first mixingstep was done in solid state. Methanol (50 mL) was added to form amixture, and mixture was stirred to dissolve the ACP. (Sulfur and ZnEDCwere not soluble in the methanol). DHL (10 g) was added to the mixtureand stirred; the resulting slurry, containing the ACP, sulfur, ZnEDC andDHL was allowed to dry overnight in the dark. The slurry was then placedin a vacuum oven at room temperature for 12 hours to ensure completeremoval of methanol. The dried, uncured polymer-carbon sample was thenground to a powdery form with mortar and pestle, to ensure an evendistribution of ZnEDC and sulfur.

To cure samples, a dried, uncured polymer-carbon sample, prepared asabove, was placed between two TEFLON sheets and pressed to a pressure atabout 4500 psi. The temperature of the heating plates was graduallyincreased from 20° C. to 130° C. (Heating Rate: 5° C./min) Thecross-linking reaction was allowed to continue at this temperature overa period of 25 min The cured polymer-carbon powder sample was thenstored at room temperature.

Cure was confirmed by DSC thermograms. In these samples, the thermogramsof uncured polymer also had peaks for melting point endotherms of twoconfirmations of sulfur, i.e., orthorhombic and monoclinic. The sulfurmelting peaks were sharper than the broad reaction endotherms. However,these melting peaks disappeared in the thermogram of a cured sample.

To determine the maximum amount of sulfur, or saturation point, for the10,000 Mn polymer, the sulfur content in a mixture was increased by 10wt % per sample, until sulfur melting point peaks appeared in the DSCthermogram of a cured sample. For this sample, the sulfur saturationpoint was obtained when sulfur reached a concentration of 60 parts per100 parts by weight polymer. DSC of thermograms of cured samples with60, 70, and 80 parts sulfur per 100 parts of polymer showed meltingpeaks for sulfur, indicating free sulfur in the samples, and thereforepast the samples' saturation point of sulfur.

EXAMPLE 4 Cure Using Lower Amount of Carbon

Sample 4 was prepared with 100 parts ACP, 100 parts DHL, 30 partssulfur, and 6 parts ZnDEC. The DSC thermogram obtained prior to curingshowed the presence of a curing endotherm, as well as sulfur meltingendotherms. The sample was cured at 130° C. for 25 minutes. Theendotherm observed in the DSC after curing did not exhibit the meltingsulfur melting endotherms, indicating that the cure was complete.

EXAMPLE 5

Modification with Thiols

Two of the polymer-carbon sorbents were modified further by reactingwith 2-mercaptoethanol. Sample 2(b), with 100 parts ACP (10,000 Mn PEI),11 parts sulfur, 1 part ZnEDC, and 200 parts DHL and Sample 3(c) with100 parts ACP (10,000 Mn PEI), 50 parts sulfur, 10 parts ZnEDC and 200parts DHL were modified to form samples 5(a) and 5(b), respectively. Thereaction with 2-mercaptoethanol was intended to cleave the disulfidelinkages in the crosslinked polymer to introduce thiol moieties. Thiolshave an affinity to react with Hg⁰ and Hg⁺². The reaction proceeds viaaddition of the mercuric ion to two thiol moieties, followed byelimination of two protons. Therefore, modifying with the2-mercaptoethanol should have increased the sorbent capture of ionicmercury.

The polymer-carbon sorbents were treated by reacting with a 10×stoichiometric excess of 2-mercaptoethanol, in a slurry for 3 hours at50° C. The slurry was rinsed in chloroform in a Büchner funnel to removeexcess 2-mercaptoethanol. These samples were used to determine theirabilities to capture Hg⁰ and Hg⁺².

EXAMPLE 6 Elemental Mercury Capture Measurement

Table 2 below shows the data for elementary mercury capture in mg Hg/gsample for the samples with high loadings of sulfur. The mercury captureof the DHL alone was 138.2 mg/g when tested alone. The data below showimprovement over the DARCO® HG LH product for many of the samples.

TABLE 2 Elemental Mercury Capture (mg/g) Parts Sulfur Mn~10000 Mn~1300Mn~2000 DARCO ® Hg—LH 50 159.5 234 284.55 145 45 376.5 298.2 315.6 14540 97.75 195.6 209.8 145 30 115.87 197.4 253.4 145

FIG. 7 shows the a graph of the milligrams (mg) mercury capture per gram(g) adsorbent as a function of the parts sulfur added for each of thenominal molecular weights (Mn 1300, 2000, and 10000) ofpoly(ethyleneimine). A line representing unmodified DHL (i.e. no sulfuradded) is drawn in for comparison. The relationship between parts sulfurand elemental mercury adsorption appears to be nonlinear.

EXAMPLE 7 Hg⁺² Capture Measurement

A 1.75×10⁻³ M aqueous solution of mercuric nitrate (10 mL) was added toa test tube (150×15) containing MAC (25 mg). The resulting heterogeneousmixture was allowed to stir at room temperature for 30 minutes. Theheterogeneous mixture was then transferred to a centrifuge tube andcentrifuged at 1228 g for 20 minutes. An aliquot was analyzed forresidual Hg⁺² using ICPMS spectrometer.

The mixture of MAC and mercuric nitrate was refluxed in a 50 mLround-bottom flask for about 30 minutes, cooled; an aliquot wascollected using the same procedure outlined above.

The DHL activated carbon captured 76.45 percent of the amount of theinitial mercury (Hg⁺²) added to the solution. Table 3 below shows thedata for Hg⁺² captured per sample in percent. The data below showimprovement over the DARCO® HG LH product for many of the samples.

TABLE 3 Mercury (II) Capture % of initial amount of Mercury added insolution Parts Sulfur Mn~1300 Mn~2000 Mn~10000 DARCO ® Hg—LH 50 52.0668.32 92.98 75 45 71.45 57.37 95.82 75 40 52.10 78.59 80.46 75 30 48.8576.35 98.65 75

FIG. 8 shows percent added Hg⁺² as HgNO₃ in deionized water as afunction of the amount of sulfur added to samples.

EXAMPLE 8 Heavy Metal Capture Measurement

Aqueous solutions of water-soluble heavy metals salts, preferablychlorides of cadmium, nickel, cobalt, chromium, and manganese, areprepared separately. The concentration of each solution is maintained at1×10⁻³ M. Ten mL of each solution is transferred into each of nine(150×15) test tubes. To each test tube, MAC (500 mg) is added and theheterogeneous solutions (three tubes in a group) are mixed for 1, 2, and3 hours, respectively, and then centrifuged (1228 G) for 5 minutes. Thesupernatants are decanted into separate test tubes. Each sample is thendiluted to 100 parts per billion (ppb) and the concentrations of heavymetals present in the supernatants are measured in triplicate (and anaverage calculated) using ICP-MS spectroscopy. Table 4 below is anexample of the heavy metal ion capturing ability of MAC from an aqueoussolution.

TABLE 4 Heavy Metal Capturing Abilities of MAC 1 Hour % 2 Hour % 3 Hour% Chloride Salt Capture Capture Capture Chromium(III) Chloride 69.8638467.61447 83.64704 Cobalt(II) Chloride 44.01192 61.66832 37.91791Manganese (II) Chloride 74.91237 89.95344 97.86125

Although the invention has been described with reference to itspreferred embodiments, those of ordinary skill in the art may, uponreading and understanding this disclosure, appreciate changes andmodifications which may be made which do not depart from the scope andspirit of the invention as described above or claimed hereafter.

What is claimed is:
 1. A process for preparing a polymer-carbon sorbentcomprising mixing and curing: a. a carbonaceous sorbent material, b. acurable amine-containing polymer, comprising contacting anamine-containing polymer having primary amine groups with an allylhalide, in the presence of a catalyst, to form a curableamine-containing polymer, comprising allyl end-groups, and secondary andtertiary amine groups, c. a sulfur agent, S₈ in its orthorhombic,monoclinic, or amorphous forms, d. a cure accelerator, and e.optionally, an activator.
 2. The process of claim 1 wherein theamine-containing polymer has a number average molecular weight fromabout 1,000 to about 10,000.
 3. The process of claim 1 wherein the cureaccelerator is a zinc salt of diethyldithiocarbamate.
 4. The process ofclaim 1 wherein the sulfur agent is in molar excess to the curableamine-containing polymer with the assumption that 10,000 g of thepolymer is 1 mole and 32 g of sulfur agent of is 1 mole.